The numerical study of hypersonic inlet flow with different inner compression surface was carried out, aimed at exploring the influence of horizontal angle of lower inlet surface on inlet performance specially restarting characteristics. The result shows that the reduction of surface horizontal angle on the tail of separation bubble will improve the performance of unstart flow and decrease the restart Mach number, with the disadvantage of increasing length of inner compression surface and reducing the performance of start flow. To optimize the synthetic performance of inlet, a new design of inner compression lower surface composed of the concave surface in the front and the straight surface with small horizontal angle in the rear was proposed. Compared with the prototype, the performance of start flow drop lightly under the same length for new inlet, but the restart Mach number of latter reduce from 9.4 to 8.